Measuring High Energy Electromagnetic Cascades in the Laboratory

Detector Layers

Particle Identification

Electromagnetic Cascade

….building a simple electromagnetic cascade model...

Radiation length The radiation length is an indicator of how far a particle travels in a medium before losing about 1/3rd of its energy.

Critical Energy A high energy electron can lose energy by emitting gamma radiation if it is deflected. Below a certain critical energy in a material, the electron no longer loses energy in this way, it simply ionises atoms or is scattered

Interaction Model

Population of Electrons in a Cascade

Eoriginal = 2t x Ecritical If the number of particles doubles at each radiation length then there should be 2t particles associated with the peak of the graph If the peak of the graph corresponds to the point where the critical energy is reached then the original energy should be given by: Eoriginal = 2t x Ecritical

We aim to: ...use GM tubes arranged to register groups of electrons …look for cascades in lead sheets caused by cosmic rays

Experimental Setup

Apparatus list 3 GM tubes and their EHT supplies 20 sheets of lead (thickness about 2 mm, size about 20 cm by 20 cm or more) laboratory tripod a three input AND gate a counter that can by driven by the AND gate a reliable clock

Setup of the Experiment

GM Tube connections to the AND gate

Prepare to plot the points as the measurements are taken...

Calculating the energy The radiation length for lead is 0. 56cm Calculating the energy The radiation length for lead is 0.56cm. Find the thickness of lead associated with the peak in the graph and work out how many radiation lengths it represents.

The critical energy for electrons in lead is about 7. 6 MeV The critical energy for electrons in lead is about 7.6 MeV. The maximum in the graph corresponds to the particles having the critical energy If there are 2t particles then the initial energy must be 2t x 7.6 MeV

You will have: - a direct measurement of the typical energy of cosmic ray particles passing through the room - made a measurement similar to the ones made many times per second in modern particle detectors

If you would now like to try building one of these…...